The invention relates to a method for producing cold-rolled strips or sheets out of low-alloyed steels with a respective max. 0.2% of C, P, Al, Ti, V, Nb, S, B and a respective max. 1% Si and Mn, remainder iron and unavoidable impurities. After being melted, the steel is cast into slabs, thin slabs or strips, generally in a continuous casting procedure, and then hot-rolled, cold-rolled and subjected to recrystallizing annealing.
The annealing temperature level required for a complete recrystallization of the cold-rolled strip or sheet can be influenced in the preliminary stages of strip steel production. For example, it is known that the recrystallization temperature can be reduced via a high hot-strip coiling temperature and a high cold-rolling ration.
The object of the invention is to reduce the production outlay and associated manufacturing costs for generating a completely recrystallized, cold-rolled strip or sheet.
To achieve this object, the invention proposes that, in the generic procedure, the slabs or strips be hot-rolled at an initial temperature exceeding 1,100xc2x0 C. and a final temperature lying under Ar3, the hot strip be coiled at a temperature lying below 650xc2x0 C., and the cold strip then be cold-rolled at a temperature which is nearly independent of the cold rolling ratio and as low as possible ranging from 500 to 750xc2x0 C. for a time sufficient to ensure complete recrystallization.
The invention is based on the surprising determination that by the use of a reduced hot-roll final temperature and a low coiling temperature a complete recrystallisation of the cold-rolled strip can be obtained at a comparatively low temperature nearly independently of the cold rolling strain. A low temperature for recrystallization annealing saves energy and costs.
In addition to the alloy contents specified above, the steels may contain 0.01% of nitrogen and the quantity of boron ( greater than 0.78xc3x97N) required for nitrogen fixation. Beyond that, slight quantities of other alloying elements that have no negative impact on the recrystallization conditions are also permissible.
If possible, the hot-roll final temperature should lie 50xc2x0 C. under Ar3, and the coiling temperature should preferably range from 300 to 600xc2x0 C. IF-steels with a low carbon content of up to 0.01% or steels micro-alloyed with Ti, V, Nb can be completely recrystallization annealed in a temperature range of 600 to 780xc2x0 C., while non-micro-alloyed steels can be completely recrystallization annealed at even lower temperatures ranging from 500 to 680xc2x0 C., largely independently of the cold rolling level.